Three-color fluorescent materials, e.g., red phosphor, blue phosphor and green phosphor, are used in a color Braun tube, a fluorescent lamp, a projection type cathode-ray tube, or the like. A color Braun tube generally comprises as its essential component a fluorescent screen coated with three-color (green G, blue B, red R) fluorescent materials which radiate by an electronic ray on an inner surface of the screen.
The process for manufacturing such a fluorescent screen is largely divided into a coating of light-absorbing black material (BM) [FIG. 1] and a coating of three-color fluorescent materials such as green phosphor, blue phosphor, and red phosphor (PH) [FIG. 2].
As illustrated in FIG. 1, the BM coating process comprises washing and drying panel (1) and then injecting and coating a photoresist thereto to form photoresist film; patterning the photoresist films to define a part to form a fluorescent film of three primary colors (R, G, B); forming a film of graphite coated on the panel (1) including the patterned photoresist film; etching the graphite coating using the patterned photoresist film as a mask; and then developing and drying thereof to form a graphite matrix (2).
Subsequently, as illustrated in FIG. 2, the inner surface of the face plate passed through the BM process as above is washed with warm, pure water and coated with a precoat, and then coated with a mixed liquid of green (or blue) fluorescent material and photoresist resin and then dried to form a green fluorescent [or blue fluorescent] material layer.
Subsequently, ultra-violet (UV) rays irradiate the green fluorescent layer [or blue fluorescent material layer] through the hole of a shadow mask.
At this time, the position of UV irradiation corresponds to the position of electron beam collision for radiating the green (or blue) fluorescent material layer, or to the position for the green (or blue) fluorescent material layer to be fixed.
Then, upon washing the panel (1) irradiated by UV with a solvent, a part cured by UV irradiation remains undissolved on the face plate surface, while the other part is dissolved and removed to form a green fluorescent film (4) [or blue fluorescent film (3)], as illustrated in FIG. 4.
Second, similar procedures are carried out as to the first process above using a mixture layer of blue fluorescent material [or green fluorescent material] and a photosensitive resin to form a blue fluorescent film (3) [or green fluorescent film (4)]. Third, similar procedures are carried out as to the first process above using a mixture of red fluorescent material and a photosensitive resin to form a red fluorescent film (5) as illustrated in FIG. 3.
After the coating the three-color fluorescent films (3), (4) and (5), an emulsion is coated in order to even an Al-deposited film to that completes the PH process.
As described above, according to the conventional process for PH coating, the red fluorescent film (5) is finally formed when the three-color fluorescent are coated on the inner surface of the face plate, having the following order of formation: green→blue→red fluorescent film or blue→green→red fluorescent film. In this case, however, upon the formation of green→blue (or blue→green) fluorescent film, flection occurs creating an uneven surface on which to form the red fluorescent film (5) on the inner surface of the panel glass (1). Thus, the distribution of the red fluorescent film (5) finally coated is not homogeneous, whereby inferiorities such as cracks, light leakage, or the like readily occur. Further, owing to the uneven thickness, white brightness, bright uniformity and white uniformity deteriorate, so that the thickness of the red fluorescent film (5) formed is thicker by about 30% than that of the green or blue fluorescent films (4) and (5), as shown in FIG. 3. The increase of the amount of the red fluorescent material used to make the red fluorescent film (5) increases the prime cost (i.e., red fluorescent material has an about a 10-fold price than that of green or blue fluorescent material).
More specifically, calculated values of optimum S/Weight (i.e., coating weight per unit area) of the fluorescent material are as follows:                A. Green fluorescent material for the greed fluorescent film (particle size: 11.5 μm, apparent density: 1.62 g/cm3)                    1) Optimum thickness of the green fluorescent film: about 1.5-fold of the particle size of the phosphor, i.e., 11.5×1.5=17.25 μm            2) Optimum S/Weight screen weight (i.e., S/Weight): 1.62 g/cm3×0.001725 cm×1000 mg/g=2.8 mg/cm2 (i.e., the weight of green fluorescent material per unit area)                        B. Blue fluorescent material for the blue fluorescent film (particle size: 11.5 μm, apparent density: 1.16 g/cm3)                    1) Optimum thickness of the blue fluorescent film: about 1.5-fold of the particle size of the phosphor, i.e., 11.5×1.5=17.25 μm            2) Optimum S/Weight: 1.16 g/cm3×0.001725 cm×1000 mg/g=2.0 mg/cm2 (i.e., the weight of blue fluorescent material per unit area)                        C. Red phosphor (particle size: 11.5 μm, apparent density: 1.66 g/cm3)                    1) Optimum thickness of the red fluorescent film: about 1.5-fold of the particle size of the phosphor, i.e., 11.5×1.5=17.25 μm            2) Optimum S/Weight: 1.66 g/cm3×0.001725 cm×1000 mg/g=2.9 mg/cm2 (i.e., the weight of red fluorescent material per unit area)                        
As can be seen form the calculated optimum S/Weight as above, the S/Weight ratio of green phosphor to red phosphor is optimum at 1.00:1.04, but the ratio of 1.00:1.30–1.50 is practically used.